Nonaqueous electrolyte secondary battery

ABSTRACT

A non-aqueous electrolyte secondary battery includes a pressure-sensitive current shut-off mechanism, wherein a positive electrode core body exposed portion is disposed at one end portion of a flat rolled electrode assembly, a negative electrode core body exposed portion is disposed at the other end portion, lithium carbonate is contained in a positive electrode mix layer, and a protective layer is disposed along the border with the positive electrode mix layer at the position opposite to a separator on the positive electrode core body exposed portion.

TECHNICAL FIELD

The present invention relates to a non-aqueous electrolyte secondarybattery.

BACKGROUND ART

On-vehicle non-aqueous electrolyte secondary batteries used as, forexample, driving power supplies for electric vehicles (EV) and hybridelectric vehicles (HEV, PHEV) are provided with pressure detection typecurrent shut-off mechanisms in addition to safety valves for explosionprotection. The pressure detection type current shut-off mechanisms isdisposed in such a way as to be actuated by a gas rapidly generated inthe inside of a battery under abnormal conditions and prevent burst orignition of the battery by shutting-off a current inflow.

As for the non-aqueous electrolyte secondary battery, an increase incharging voltage has been known as one of techniques to increase thebattery capacity. Also, it is known that an overcharge inhibitor, e.g.,tert-amylbenzene, biphenyl (refer to PTL 1), cycloalkylbenzenecompounds, or compounds having quaternary carbon adjacent to a benzenering (refer to PTL 2), is added to a non-aqueous electrolytic solutionas a safety measure when a non-aqueous electrolyte secondary battery isbrought into an overcharge state. However, if the charging voltage isincreased to improve the battery capacity, the overcharge inhibitor isdecomposed even at a voltage set as a usual working range depending onthe type of the overcharge inhibitor, so that degradation of batterycharacteristics and degradation of safety after charge-discharge cycleare feared.

It is also known that in order to solve such issues, the overchargeresistance is improved by adding lithium carbonate (Li₂CO₃) to apositive electrode mix of the non-aqueous electrolyte secondary battery(PTL 3). In the case where lithium carbonate is added to the positiveelectrode mix of the non-aqueous electrolyte secondary battery, when ahigh voltage is applied to the battery, for example, at the time ofovercharge, carbon dioxide gas is generated from a positive electrodeplate and, thereby, the pressure detection type current shut-offmechanism can be actuated reliably prior to the safety valve forexplosion protection.

CITATION LIST Patent Document

-   PTL 1: International Publication No. 2002/059999-   PTL 2: Japanese Published Unexamined Patent Application No.    2008-186792-   PTL 3: Japanese Published Unexamined Patent Application No.    04-328278

SUMMARY OF INVENTION Technical Problem

The non-aqueous electrolyte secondary battery includes a rolledelectrode assembly in which a positive electrode plate and a negativeelectrode plate are rolled in the state of being insulated from eachother by a separator. In a flat rolled electrode assembly, the borderportion between a positive electrode core body and a positive electrodemix layer is covered with a separator. However, the separator isflexible and, therefore, the border portion between the positiveelectrode core body and the positive electrode mix layer is denselycovered with the separator.

In such a situation, if an overcharge state is brought about and a gasis generated on the surface of the positive electrode plate, theresulting gas is not easily moved to the outside of the flat rolledelectrode assembly through the border portion between the positiveelectrode core body and the positive electrode mix layer and, therefore,remains on the surface of the positive electrode plate in the flatrolled electrode assembly. A current does not pass through the placewhere the gas is present on the surface of the positive electrode plate,so that the overcharge state is eliminated. However, in the place wherethe gas is not present on the surface of the positive electrode plate,the overcharge state is further facilitated.

Solution to Problem

According to a non-aqueous electrolyte secondary battery of an aspect ofthe present invention,

a non-aqueous electrolyte secondary battery is provided including:

a positive electrode plate in which a positive electrode mix layer isdisposed on a positive electrode core body;

a negative electrode plate in which a negative electrode mix layer isdisposed on a negative electrode core body;

a positive electrode terminal electrically connected to theabove-described positive electrode plate;

a negative electrode terminal electrically connected to theabove-described negative electrode plate;

a flat rolled electrode assembly in which the above-described positiveelectrode plate and the above-described negative electrode plate in thestate of being insulated from each other with a separator therebetweenare rolled into a flat shape;

a non-aqueous electrolytic solution; and

an outer body,

wherein a rolled positive electrode core body exposed portion isdisposed at one end portion of the above-described flat rolled electrodeassembly,

a rolled negative electrode core body exposed portion is disposed at theother end portion of the above-described flat rolled electrode assembly,

the above-described rolled positive electrode core body exposed portionis bundled and connected to a positive electrode collector,

the above-described rolled negative electrode core body exposed portionis bundled and connected to a negative electrode collector,

a pressure-sensitive current shut-off mechanism is disposed in at leastone of a conducting path between the above-described positive electrodeplate and the above-described positive electrode terminal and aconducting path between the above-described negative electrode plate andthe above-described negative electrode terminal,

lithium carbonate is contained in the above-described positive electrodemix layer, and

a porous protective layer is disposed along the border with theabove-described positive electrode mix layer at the position opposite tothe above-described separator on at least one surface of theabove-described positive electrode core body exposed portion.

Advantageous Effects of Invention

In the non-aqueous electrolyte secondary battery according to an aspectof the present invention, lithium carbonate is contained in the positiveelectrode mix layer, and the porous protective layer is disposed alongthe border with the positive electrode mix layer at the positionopposite to the separator on at least one surface of the positiveelectrode core body exposed portion. In this regard, the protectivelayer only needs to be disposed on at least one surface of the positiveelectrode core body exposed portion, although may be disposed on bothsurfaces. Furthermore, in the case where the positive electrode corebody exposed portions are disposed on both sides in the width directionof the positive electrode, the protective layers may be disposed on thepositive electrode core body exposed portions of both sides.

This protective layer forms an airway in the rolling axis directionbetween the protective layer and the separator on the basis of a heightdifference formed between the positive electrode core body exposedportion and the positive electrode mix layer and, in addition, hasbreathability to pass a gas. Consequently, carbon dioxide gas generatedby decomposition of lithium carbonate in the positive electrode mixlayer at the time of overcharge is allowed to flow to the outside of theflat rolled electrode assembly through the inside of the protectivelayer easily. Therefore, according to the non-aqueous electrolytesecondary battery of an aspect of the present invention, carbon dioxidegas is not retained on the surface of the positive electrode mix layereasily, so that a pressure-sensitive current shut-off mechanism isallowed to be promptly reliably actuated before the internal pressure ofthe battery increases to a great extent and the safety at the time ofovercharge becomes very good.

In this regard, the protective layer only needs to be disposed along theextension direction of the border between the positive electrode corebody exposed portion and the positive electrode mix layer on thepositive electrode core body exposed portion. The protective layer maybe disposed in such a way as to come into contact with the positiveelectrode mix layer. Alternatively, the protective layer may be disposedat a distance from the positive electrode mix layer and, therefore, at aposition apart from the positive electrode mix layer.

In this regard, the porosity of the protective layer is preferablyspecified to be larger than the porosity of the positive electrode mixlayer. Consequently, carbon dioxide gas flows to the outside of the flatrolled electrode assembly through the inside of the protective layermore easily. Also, the thickness of the protective layer is preferablyspecified to be less than the thickness of the positive electrode mixlayer. Preferably, the protective layer contains an inorganic oxide anda binder. Preferable examples of inorganic oxides include alumina,titania, zirconia, and silica. The binder is not specifically limited,although resin binders are preferable and, particularly preferably,polyvinylidene fluoride is used. Also, the protective layer may furthercontain an electrically conductive material, e.g., a carbon material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a non-aqueous electrolyte secondary batteryaccording to an embodiment, and FIG. 1B is a front view of the same.

FIG. 2A is a partial sectional view along a line IIA-IIA shown in FIG.1A, FIG. 2B is a partial sectional view along a line IIB-IIB shown inFIG. 2A, and FIG. 2C is a partial sectional view along a line IIC-IICshown in FIG. 2A.

FIG. 3A is a plan view of a positive electrode plate used for anon-aqueous electrolyte secondary battery in an embodiment, and FIG. 3Bis a plan view of a negative electrode plate used for the same.

FIG. 4A is a perspective view in which a rolling end side of a flatrolled electrode assembly according to an embodiment is developed, FIG.4B is a magnified sectional view along a line IVB-IVB shown in FIG. 4A,and FIG. 4C is a magnified sectional view of a portion corresponding to4B after attachment of a positive electrode collector following therolling.

FIG. 5 is a plan view of a positive electrode plate corresponding to acomparative example.

FIG. 6A is a perspective view in which a rolling end side of a flatrolled electrode assembly according to a comparative example isdeveloped, FIG. 6B is a magnified sectional view along a width directionof the positive electrode late in FIG. 6A, and FIG. 6C is a magnifiedsectional view of a portion corresponding to 6B after attacluent of apositive electrode collector following the rolling.

FIG. 7 is a sectional view of a non-aqueous electrolyte secondarybattery provided with a forced short-circuit mechanism.

FIG. 8A is a diagram showing the state before actuation of a forcedshort-circuit mechanism, and FIG. 8B is a diagram showing the stateafter actuation of the forced short-circuit mechanism.

DESCRIPTION OF EMBODIMENTS

The embodiments according to the present invention will be describedbelow in detail with reference to the drawings. However, each of theembodiments described below is an exemplification for the sake ofunderstanding the technical idea of the present invention and is notintended to specify the present invention to the embodiment. The presentinvention can be equally applied to various modifications withoutdeparting from the technical ideas shown in the claims.

[Embodiments]

To begin with, a non-aqueous electrolyte secondary battery according toan embodiment is described with reference to FIG. 1 to FIG. 4. As shownin FIG. 4, this non-aqueous electrolyte secondary battery 10 includes aflat rolled electrode assembly 14 in which a positive electrode plate 11and a negative electrode plate 12 in the state of being insulated fromeach other with a separator 13 therebetween are rolled. The outermostsurface side of this flat rolled electrode assembly is covered with theseparator 13, and the negative electrode plate 12 is arranged on theside nearer to the outer circumference than the positive electrode plate11 is.

As shown in FIG. 3A, a positive electrode mix layer 11 a is disposed onboth surfaces of a positive electrode core body made of aluminum oraluminum alloy foil having a thickness of about 10 to 20 μm in such away that the positive electrode core body comes into the state of beingexposed in the shape of a belt along the end portion on one side in thewidth direction. This positive electrode core body portion exposed inthe shape of a belt serves as a positive electrode core body exposedportion 15. A protective layer 11 b is disposed along the lengthdirection of the positive electrode core body exposed portion 15 on atleast one surface of the positive electrode core body exposed portion 15in such a way as to, for example, adjoin the positive electrode mixlayer 11 a. The specific configuration and the like of this protectivelayer 11 b will be described later.

In the negative electrode plate 12, as shown in FIG. 3B, a negativeelectrode mix layer 12 a is disposed on both surfaces of a negativeelectrode core body made of copper or copper alloy foil having athickness of about 5 to 15 μm in such a way that the negative electrodecore body is brought into the state of being exposed in the shape of abelt along the end portion on one side in the width direction. Thisnegative electrode core body portion exposed in the shape of a beltserves as a negative electrode core body exposed portion 16. In thisregard, the positive electrode core body exposed portion 15 or thenegative electrode core body exposed portion 16 may be disposed alongend portions on both sides of the width direction of the positiveelectrode plate 11 or the negative electrode plate 12, respectively.

These positive electrode plate 11 and negative electrode plate 12 areshifted in such a way that the positive electrode core body exposedportion 15 and the negative electrode core body exposed portion 16 donot overlap the mix layers of the respective opposite electrodes and arerolled into a flat shape while being insulated from each other with theseparator 13 therebetween, so that the flat rolled electrode assembly 14is produced. As shown in FIG. 2A, FIG. 2B, and FIG. 4A, the flat rolledelectrode assembly 14 is provided with a plurality of positive electrodecore body exposed portions 15 stacked at one end and a plurality ofnegative electrode core body exposed portions 16 stacked at the otherend. As for the separator 13, preferably, two sheets of polyolefin fineporous films or one folded long sheet is used. The width thereof is suchan extent that the positive electrode mix layer 11 a and the protectivelayer 11 b can be covered and the width larger than the width of thenegative electrode mix layer 12 a is employed.

The plurality of positive electrode core body exposed portions 15 arestacked and are electrically connected to a positive electrode terminal18 through a positive electrode collector 17. A current shut-offmechanism 27 to be actuated by a pressure of gas generated in the insideof the battery is disposed between the positive electrode collector 17and the positive electrode terminal 18. The plurality of negativeelectrode core body exposed portions 16 are stacked and are electricallyconnected to a negative electrode terminal 20 through a negativeelectrode collector 19.

As shown in FIG. 1A, FIG. 1B, and FIG. 2A, the positive electrodeterminal 18 and the negative electrode terminal 20 are fixed to asealing body 23 through insulating members 21 and 22, respectively. Thesealing body 23 is also provided with a gas discharge valve 28 to beopened when a gas pressure higher than the actuation pressure of thecurrent shut-off mechanism 27 is applied. Each of the positive electrodecollector 17, the positive electrode terminal 18, and the sealing body23 is made of aluminum or an aluminum alloy and is used. Each of thenegative electrode collector 19 and the negative electrode terminal 20is made of copper or a copper alloy and is used.

The flat rolled electrode assembly 14 surrounded by an insulating sheet24, which is made of a resin material, excluding the sealing body 23side is inserted into a rectangular outer body 25, in which one face isopened. The rectangular outer body 25 is made of, for example, aluminumor an aluminum alloy and is used. The sealing body 23 is fit into anopening portion of the rectangular outer body 25, and the fittingportion of the sealing body 23 and the rectangular outer body 25 islaser welded. A non-aqueous electrolytic solution is poured into therectangular outer body 25 from an electrolytic solution injection hole26. This electrolytic solution injection hole 26 is hermetically sealedwith, for example, a blind rivet.

The non-aqueous electrolyte secondary battery 10 is used for varioususes alone or in combination, where a plurality of batteries areconnected in series, in parallel, or in series and parallel. In thisregard, in the case where a plurality of non-aqueous electrolytesecondary batteries 10 are connected in series or in parallel foron-vehicle uses and the like, it is favorable that a positive electrodeexternal terminal and a negative electrode external terminal aredisposed separately and individual batteries are connected with a busbar.

The flat rolled electrode assembly 14 used in the non-aqueouselectrolyte secondary battery 10 according to the embodiment is used forapplications where a high battery capacity of 20 Ah or more and highoutput characteristics are required and, for example, the number ofrolling of the positive electrode plate 11 is 43, that is, the totalnumber of stacked sheets of the positive electrode plate 11 is a large86. In this regard, in the case where the number of rolling is 15 ormore, that is, the total number of stacked sheets is 30 or more, thebattery capacity can be specified to be 20 Ah or more without upsizingthe battery excessively.

If the total number of stacked sheets of the positive electrode corebody exposed portions 15 or the negative electrode core body exposedportions 16 is large, as described above, in the case where the positiveelectrode collector 17 is attached to the positive electrode core bodyexposed portions 15 or the negative electrode collector 19 is attachedto the negative electrode core body exposed portions 16 by resistancewelding, a large welding current is required to form a weld trace 15 aor a weld trace 16 a which penetrates the entire stacked portion of theplurality of positive electrode core body exposed portions 15 ornegative electrode core body exposed portions 16.

Consequently, as shown in FIG. 2A to FIG. 2C, on the positive electrodeplate 11 side, the plurality of positive electrode core body exposedportions 15 are stacked by rolling, are bundled to the central portionin the thickness direction, and are further divided into two parts. Eachpart is bundled centering one-quarter of the thickness of the flatrolled electrode assembly and a positive electrode intermediate member30 is disposed between the two parts. In the positive electrodeintermediate member 30, a plurality of, for example, two electricallyconductive positive electrode electrically conductive members 29 areheld by a base member made of a resin material. The positive electrodeelectrically conductive members 29 having, for example, the shape of acircular column are used, and each of them is provided withfrusto-conical protrusions, which function as projection, on the sideopposite to the stacked positive electrode core body exposed portions15.

On the negative electrode plate 12 side, the plurality of negativeelectrode core body exposed portions 16 are stacked by rolling, arebundled to the central portion in the thickness direction, and arefurther divided. Each part is bundled centering one-quarter of thethickness of the flat rolled electrode assembly and a negative electrodeintermediate member 32 is disposed between the parts. In the negativeelectrode intermediate member 32, a plurality of electrically conductivenegative electrode electrically conductive members 31, here two members,are held by a base member made of a resin material. The negativeelectrode electrically conductive members 31 having, for example, theshape of a circular column are used, and each of them is provided withfrusto-conical protrusions, which function as projection, on the sideopposite to the stacked negative electrode core body exposed portions16.

Meanwhile, the positive electrode collector 17 is disposed on each ofoutermost surfaces on both sides of the positive electrode core bodyexposed portions 15 located at both sides of the positive electrodeelectrically conductive member 29. The negative electrode collector 19is disposed on each of outermost surfaces on both sides of the negativeelectrode core body exposed portions 16 located at both sides of thenegative electrode electrically conductive member 31. In this regard,the positive electrode electrically conductive member 29 is preferablymade of aluminum or aluminum ally which is the same material as thematerial for the positive electrode core body. The negative electrodeelectrically conductive member 31 is preferably made of copper or acopper alloy which is the same material as the material for the negativeelectrode core body. The shapes of the positive electrode electricallyconductive member 29 and the negative electrode electrically conductivemember 31 may be the same or be different.

The resistance welding method by using the positive electrode core bodyexposed portions 15, the positive electrode collector 17, and thepositive electrode intermediate member 30 having the positive electrodeelectrically conductive members 29 of the flat rolled electrode assembly14 according to the embodiment and the resistance welding method byusing the negative electrode core body exposed portions 16, the negativeelectrode collector 19, and the negative electrode intermediate member32 having the negative electrode electrically conductive member 31 havealready been known. Therefore, detailed explanations thereof will not beprovided.

In the case where the positive electrode core body exposed portions 15or the negative electrode core body exposed portions 16 is divided intotwo parts, as described above, the welding current required for forminga weld trace which penetrates the entire stacked portion of theplurality of positive electrode core body exposed portions 15 ornegative electrode core body exposed portion 16 can be lower than thatin the case where division into two parts is not performed.Consequently, generation of spatter during the resistance welding issuppressed, and occurrences of troubles, e.g., internal short-circuit ofthe flat rolled electrode assembly 14 resulting from spatters, aresuppressed. In FIG. 2A, two weld traces 33 formed on the positiveelectrode collector 17 by resistance welding are shown and two weldtraces 34 on the negative electrode collector 19 are shown.

Next, specific manufacturing methods or compositions of the positiveelectrode plate 11, the negative electrode plate 12, the protectivelayer 11 b, the flat rolled electrode assembly 14, and the non-aqueouselectrolytic solution in the non-aqueous electrolyte secondary battery10 according to the embodiment will be described.

[Production of Positive Electrode Plate]

As for the positive electrode active material, a lithium nickel cobaltmanganese complex oxide represented by LiNi_(0.35)Co_(0.35)Mn_(0.30)O₂was used. This lithium nickel cobalt manganese complex oxide, a carbonpowder serving as an electrically conductive agent, and polyvinylidenefluoride (PVdF) serving as a binder were weighed in such a way that themass ratio became 88:9:3, lithium carbonate was further mixed in anamount of 1 percent by mass relative to the total amount of them, andN-methyl-2-pyrrolidone (NMP) serving as a dispersion medium was mixed,so that a positive electrode mix slurry was prepared.

The content of lithium carbonate in the positive electrode mix ispreferably 0.1 to 5.0 percent by mass. If the content of lithiumcarbonate in the positive electrode mix is less than 0.1 percent bymass, generation of carbon dioxide gas from lithium carbonate is at alow level and the current shut-off mechanism is not easily promptlyactuated. If the content of lithium carbonate in the positive electrodemix is more than 5.0 percent by mass, the proportion of lithiumcarbonate not involved in an electrode reaction excessively increases,so that reduction in the battery capacity is facilitated.

Subsequently, an alumina powder, graphite serving as an electricallyconductive agent, polyvinylidene fluoride (PVdF) serving as a binder,and N-methylpyrrolidone (NMP) serving as a solvent were kneaded in sucha way that the mass ratio of alumina powder:graphite:PVdF became83:3:14, so that a protective layer slurry was produced.

Aluminum foil having a thickness of 15 μm was used as the positiveelectrode core body, and the positive electrode mix slurry and theprotective layer slurry produced by the above-described method wereapplied to both surfaces of the positive electrode core body with a diecoater. The positive electrode mix slurry and the protective layerslurry were applied to the positive electrode core body at the sametime. Therefore, the positive electrode mix slurry and the protectivelayer slurry were joined in the vicinity of the discharge hole in theinside of the die head and are applied, so that the positive electrodemix layer 11 a and the protective layer 11 b (for example, width 7 mm)composed of a porous alumina layer containing graphite were formed. Inthis regard, one end portion in the longitudinal direction of thepositive electrode core body (end portions in the same direction of bothsurfaces) was not coated with the slurry and the positive electrode corebody was exposed, so that the positive electrode core body exposedportion 15 was formed. Then, drying was performed to remove NMP servingas the dispersion medium, compression was performed by roll press toensure a predetermined thickness, and the resulting polar plate was cutinto a predetermined dimension specified in advance.

The width of the protective layer 11 b is preferably specified to bewithin the range in which the entire surface of the protective layer 11b is not covered with the separator 13 disposed oppositely in formationof the flat rolled electrode assembly. Also, the thickness of theprotective layer 11 b is preferably specified to be less than or equalto the thickness of the positive electrode mix layer 11 a because if thethickness is larger than the thickness of the positive electrode mixlayer 11 a, reduction in the battery capacitor is caused. In thisregard, the protective layer 11 b is a porous layer and, therefore, is abreathable protective layer capable of passing a gas and the likesmoothly. The configuration of the thus produced positive electrodeplate 11 is as shown in FIG. 3A.

[Production of Negative Electrode Plate]

The negative electrode plate was produced as described below. A negativeelectrode mix slurry was prepared by dispersing 98 parts by mass ofgraphite powder, 1 part by mass of carboxymethyl cellulose (CMC), and 1part by mass of styrene-butadiene rubber (SBR) into water. One endportion in the longitudinal direction of the die negative electrode corebody of both surfaces (end portions in the same direction of bothsurfaces) of the negative electrode core body made of copper foil havinga thickness of 10 μm was not coated with the resulting negativeelectrode mix slurry and the core body was exposed, so that the negativeelectrode core body exposed portion 16 was formed. Then, drying wasperformed, compression was performed by roll press to ensure apredetermined thickness, and the resulting polar plate was cut into apredetermined dimension specified in advance, so that the negativeelectrode plate 12 commonly used in the embodiment and a comparativeexample was produced. The configuration of the thus produced negativeelectrode plate 12 is as shown in FIG. 3B.

[Preparation of Non-Aqueous Electrolytic Solution]

In the non-aqueous electrolytic solution used, 1 mol/L of LiPF₆ servingas an electrolyte salt was added to a mixed solvent in which ethylenecarbonate (EC) and methyl ethyl carbonate (MEC) serving as solvents weremixed at a ratio of 3:7 on a volume ratio (25° C., 1 atm) basis and 0.3percent by mass of vinylene carbonate (VC) was added relative to thetotal mass of non-aqueous electrolytes.

[Production of Flat Rolled Electrode Assembly]

The negative electrode plate 12 and the positive electrode plate 11produced as described above were rolled in such a way that the outermostsurface side was the negative electrode plate 12 and the positiveelectrode plate 11 and the negative electrode plate 12 were insulatedfrom each other with the separator 13 therebetween. Thereafter, forminginto the flat shape was performed, so that the flat rolled electrodeassembly 14 was produced.

The arrangement relationship between the positive electrode core bodyexposed portion 15 and the separator 13 in the positive electrode plate11 just after formation of the flat rolled electrode assembly 14 is asshown in FIG. 4B, so that a sufficient gap is formed between thepositive electrode core body exposed portion 15 and the separator 13.Meanwhile, after the positive electrode collector is attached to thepositive electrode core body exposed portions 15, the plurality ofpositive electrode core body exposed portions 15 stacked are compressedand, thereby, as shown in FIG. 4C, the gap between the positiveelectrode core body exposed portion 15 and the separator 13 becomesnarrow. However, the breathability between the positive electrode mixlayer 11 a and the outside of the flat rolled electrode assembly 14 isfavorably ensured because of presence of the protective layer 11 b onthe positive electrode core body exposed portion 15.

In particular, in the case where the width of the protective layer 11 bis specified to be within the range in which the entire surface of theprotective layer 11 b is not covered with the separator 13 disposedoppositely, the breathability between the positive electrode mix layer11 a and the outside of the flat rolled electrode assembly 14 is alwaysfavorably ensured. Therefore, in the case where the non-aqueouselectrolyte secondary battery 10 is brought into an overcharge state andcarbon dioxide gas is generated by decomposition of lithium carbonate inthe positive electrode mix layer 11 a, the resulting carbon dioxide gasis released to the outside of the flat rolled electrode assembly 14through the protective layer 11 b easily.

Consequently, according to the non-aqueous electrolyte secondary battery10 of the present embodiment, carbon dioxide gas is not retained on thesurface of the positive electrode mix layer 11 a easily, so that thepressure-sensitive current shut-off mechanism 27 (refer to FIG. 2A) isallowed to be promptly reliably actuated before the internal pressure ofthe battery increases to a great extent. When the pressure-sensitivecurrent shut-off mechanism 27 is actuated, a charging current does notflow, so that generation of carbon dioxide gas thereafter is stopped.Therefore, the internal pressure of the non-aqueous electrolytesecondary battery 10 does not increase and the safety at the time ofovercharge becomes very good.

[Comparative Example]

The specific configuration of a non-aqueous electrolyte secondarybattery according to a comparative example will be described withreference to FIG. 5 and FIG. 6. The specific configuration of thenon-aqueous electrolyte secondary battery according to the comparativeexample is substantially the same as the configuration of thenon-aqueous electrolyte secondary battery 10 according to the embodimentexcept the configuration of the positive electrode plate. Therefore,FIG. 1 and FIG. 2 are cited appropriately and, in addition, the sameconfiguration portions as those in the non-aqueous electrolyte secondarybattery according to the embodiment are indicated by the same referencenumerals and detailed explanations thereof will not be provided.

As shown in FIG. 5 and FIG. 6, the non-aqueous electrolyte secondarybattery according to the comparative example has the same configurationas the configuration of the positive electrode plate 11 according to theembodiment except that the positive electrode plate 11A does not includethe protective layer 11 b in the positive electrode plate 11 accordingto the embodiment. The configuration of the rolling end side of a flatrolled electrode assembly 14A in the comparative example is as shown inFIG. 6A.

The arrangement relationship between a positive electrode core bodyexposed portion 15 and a separator 13 in the positive electrode plate11A just after formation of the flat rolled electrode assembly 14A is asshown in FIG. 6B, so that a sufficient gap is formed between thepositive electrode core body exposed portion 15 and the separator 13.However, after a positive electrode collector is attached to thepositive electrode core body exposed portions 15, a plurality ofpositive electrode core body exposed portions 15 stacked are compressedand, thereby, the arrangement relationship between the positiveelectrode core body exposed portion 15 and the separator 13 is as shownin FIG. 6C. Consequently, the gap between the positive electrode corebody exposed portion 15 and the separator 13 becomes very narrow.

Therefore, in the non-aqueous electrolyte secondary battery according tothe comparative example, in the case where an overcharge state isbrought about and carbon dioxide gas is generated by decomposition oflithium carbonate in a positive electrode mix layer 11 a, the resultingcarbon dioxide gas tends to retain on the surface side of the positiveelectrode mix layer 11 a. In a place where carbon dioxide gas is presenton the surface of the positive electrode mix layer 11 a, a current doesnot flow and, therefore, the overcharge state is eliminated. However, inthe place where carbon dioxide gas is not present on the surface of thepositive electrode mix layer 11 a, the current continues to flow and,therefore, the overcharge state is further facilitated. Consequently,according to the non-aqueous electrolyte secondary battery of thecomparative example, the safety is insufficient as compared with thenon-aqueous electrolyte secondary battery 10 according to theembodiment.

As for the non-aqueous electrolyte secondary battery 10 according to theembodiment, the example in which fine particles made of the mixture ofalumina and graphite are used as the material for forming the protectivelayer 11 b has been shown. In addition, fine particles of at least oneselected from alumina, silicon dioxide, and titanium oxide or fineparticles of a mixture of graphite and at least one selected fromalumina, silicon dioxide, and titanium oxide can be used. In particular,in the case where alumina fine particles and graphite fine particles areused, the adhesion to the positive electrode core body or positiveelectrode mix layer is good. The range of particle diameter of thematerial for forming the positive electrode 11 b has no criticallimitation and can be arbitrarily selected within the range in which thethickness of the resulting protective layer 11 b is smaller than thethickness of the positive electrode mix layer 11 a.

As for the non-aqueous electrolyte secondary battery 10 according to theembodiment, the example in which the protective layer 11 b is disposedadjoining the positive electrode mix layer 11 a has been shown. However,the protective layer 11 b may be disposed at the position apart from thepositive electrode mix layer 11 a in such a way that a gap is generatedbetween the positive electrode mix layer 11 a and the protective layer11 b. Employment of such a configuration can easily bring about a statein which the surface of the protective layer 11 b is not covered withthe separator 13 disposed oppositely, the movability of carbon dioxidegas becomes good and, therefore, the above-described effects are exertedparticularly favorably.

As for the non-aqueous electrolyte secondary battery 10 according to theembodiment, the example in which the positive electrode core bodyexposed portion 15 is formed on only one end portion in the widthdirection of the positive electrode plate 11 and the protective layer 11b is formed at only the end portion on this side has been shown.However, the positive electrode core body exposed portions may be formedon both end portions in the width direction of the positive electrodeplate 11 and a protective layer may be formed on each of the positiveelectrode core body exposed portions.

In the above-described embodiment, it is possible that a layer havingelectrical conductivity is formed, where the electrical conductivity islower than the electrical conductivity of the positive electrode corebody, as a protective layer and lithium carbonate is contained in theresulting protective layer. In this case, preferably, the protectivelayer contains a binder, a carbon material, and at least one selectedfrom alumina, silica, titania, and zirconia. In this regard, in the casewhere each of the positive electrode mix layer and the protective layercontains lithium carbonate, the total amount of lithium carbonate ispreferably 0.1 percent by mass or more and 5 percent by mass or lessrelative to the total mass of positive electrode active material in thepositive electrode mix layer.

[Second Invention]

In the above-described embodiment, the form in which the positiveelectrode mix layer is allowed to contain lithium carbonate has beendescribed. In the second embodiment, the protective layer is allowed tocontain lithium carbonate instead of allowing the positive electrode mixlayer to contain lithium carbonate. In this case, the protective layeris specified to have the electrical conductivity, where the electricalconductivity is lower than the electrical conductivity of the positiveelectrode core body.

A rectangular non-aqueous electrolyte secondary battery according to thesecond invention includes:

a positive electrode plate in which a positive electrode mix layer isdisposed on a positive electrode core body;

a negative electrode plate in which a negative electrode mix layer isdisposed on a negative electrode core body;

a positive electrode terminal electrically connected to theabove-described positive electrode plate;

a negative electrode terminal electrically connected to theabove-described negative electrode plate;

a flat rolled electrode assembly in which the above-described positiveelectrode plate and the above-described negative electrode plate in thestate of being insulated from each other with a separator therebetweenare rolled into a flat shape;

a non-aqueous electrolytic solution; and

an outer body,

wherein a rolled positive electrode core body exposed portion isdisposed at one end portion of the above-described flat rolled electrodeassembly,

a rolled negative electrode core body exposed portion is disposed at theother end portion of the above-described flat rolled electrode assembly,

the above-described rolled positive electrode core body exposed portionis bundled and connected to a positive electrode collector,

the above-described rolled negative electrode core body exposed portionis bundled and connected to a negative electrode collector,

a pressure-sensitive current shut-off mechanism is disposed in at leastone of a conducting path between the above-described positive electrodeplate and the above-described positive electrode terminal and aconducting path between the above-described negative electrode plate andthe above-described negative electrode terminal, and

a semiconducting protective layer containing lithium carbonate isdisposed along the border with the above-described positive electrodemix layer at the position opposite to the above-described separator onat least one surface of the above-described positive electrode core bodyexposed portion.

In this non-aqueous electrolyte secondary battery, lithium carbonate iscontained in the semiconducting protective layer, and the semiconductingprotective layer is disposed along the border with the positiveelectrode mix layer at the position opposite to the separator on atleast one surface of the positive electrode core body exposed portion.In this regard, the term “semiconducting” is used in the sense of havingsuch a level of electrical conductivity that can maintain lithiumcarbonate contained in the semiconducting protective layer at a positiveelectrode potential and there is no need to have such a level ofelectrical conductivity that a metal has. This semiconducting protectivelayer may be disposed on at least one surface of the positive electrodecore body exposed portion, although may be formed on both surfaces.Furthermore, in the case where the positive electrode core body exposedportions are disposed on both sides in the width direction of thepositive electrode, the semiconducting protective layers may be disposedon the positive electrode core body exposed portions on both sides. Itis preferable that the semiconducting protective layer be disposed alongthe extension direction of the border between the positive electrodecore body exposed portion and the positive electrode mix layer on thepositive electrode core body exposed portion in such a way as to comeinto contact with the positive electrode mix layer.

The semiconducting protective layer is maintained at the same potentialas the potential of the positive electrode core body exposed portion.Therefore, when the positive electrode potential increases at the timeof overcharge and the like, lithium carbonate contained in thesemiconducting protective layer is decomposed and carbon dioxide gas isgenerated. In such a form, carbon dioxide gas does not retain in theflat rolled electrode assembly easily and flows to the outside of theflat rolled electrode assembly easily as compared with the form in whichlithium carbonate contained in the positive electrode mix layer isdecomposed and carbon dioxide gas is generated. Therefore, nonuniformityin the reaction due to retention of the gas between the positiveelectrode and the negative electrode can be suppressed and thepressure-sensitive current shut-off mechanism can be actuated moresafely, so that the safety at the time of overcharge is very good.

Preferably, the semiconducting protective layer is porous in such a waythat the gas can be passed. Also, the porosity of the semiconductingprotective layer is preferably larger than the porosity of the positiveelectrode mix layer. Consequently, carbon dioxide gas generated bydecomposition of lithium carbonate in the semiconducting protectivelayer at the time of overcharge flows to the outside of the flat rolledelectrode assembly easily.

In this regard, the thickness of the semiconducting protective layer isspecified to be preferably less than or equal to the thickness of thepositive electrode mix layer, and more preferably less than thethickness of the positive electrode mix layer. The semiconductingprotective layer may be disposed adjoining the positive electrode mixlayer. Alternatively, the semiconducting protective layer may bedisposed at the position apart from the positive electrode mix layer. Inthe case where the semiconducting protective layer is disposed at theposition apart from the positive electrode mix layer, a state in whichthe surface of the semiconducting protective layer is not covered withthe separator disposed oppositely can be brought about easily, themovability of carbon dioxide gas becomes good and, therefore, theabove-described effects are exerted particularly favorably.

Preferably, the semiconducting protective layer contains fine particlesof a mixture of graphite and at least one selected from alumina, silicondioxide, and titanium oxide. Preferably, the semiconducting protectivelayer is disposed in such a way that a region not covered with theseparator disposed oppositely is generated. In the case where the widthof the semiconducting protective layer is specified to be within therange in which the entire surface of the semiconducting protective layeris not covered with the separator disposed oppositely, the breathabilitybetween the positive electrode mix layer and the outside of the flatrolled electrode assembly is always favorably ensured. Therefore, in thecase where the non-aqueous electrolyte secondary battery is brought intoan overcharge state and carbon dioxide gas is generated by decompositionof lithium carbonate in the semiconducting protective layer, theresulting carbon dioxide gas is released to the outside of the flatrolled electrode assembly through the semiconducting protective layereasily. The amount of lithium carbonate in the semiconducting protectivelayer is preferably 0.1 percent by mass or more and 5 percent by mass orless relative to the total mass of the positive electrode activematerial in the positive electrode mix layer.

The non-aqueous electrolyte secondary battery according to the secondinvention can be substantially the same as the non-aqueous electrolytesecondary battery 10 according to the above-described embodiment exceptthat the configurations of the positive electrode mix slurry and thesemiconducting protective layer slurry used in production of thepositive electrode plate are different. Methods for manufacturing thepositive electrode mix slurry and the semiconducting protective layerslurry will be described below.

[Positive Electrode Mix Slurry]

The positive electrode mix slurry is produced by the same method as themethod of the above-described embodiment except that lithium carbonateis not added.

[Semiconducting Protective Layer Slurry]

An alumina powder, graphite serving as an electrically conductive agent,polyvinylidene fluoride (PVdF) serving as a binder, lithium carbonate,and N-methylpyrrolidone (NMP) serving as a solvent are kneaded in such away that the mass ratio of alumina powder:graphite:lithiumcarbonate:PVdF becomes 82:3:1:14, so that a semiconducting protectivelayer slurry is produced.

In the above-described method for manufacturing the semiconductingprotective layer slurry, the example in which fine particles made of themixture of alumina and graphite are used as the material for forming thesemiconducting protective layer has been shown. However, fine particlesof a mixture of graphite and at least one selected from alumina, silicondioxide, and titanium oxide can also be used. In particular, in the casewhere alumina fine particles and graphite fine particles are used, theadhesion to the positive electrode core body or positive electrode mixlayer is good. The range of particle diameter of the material forforming the semiconducting protective layer has no critical limitationand can be arbitrarily selected within the range in which the thicknessof the resulting protective layer is smaller than the thickness of thepositive electrode mix layer. The positive electrode core body exposedportion may be formed on only one end portion in the width direction ofthe positive electrode plate and the semiconducting protective layer maybe formed at only the end portion on this side. Alternatively, thepositive electrode core body exposed portions may be formed on bothsides in the width direction of the positive electrode plate and asemiconducting protective layer may be formed on each of the positiveelectrode core body exposed portions.

Preferably, the semiconducting protective layer is specified to be alayer having electrical conductivity, where the electrical conductivityis lower than the electrical conductivity of the positive electrode corebody. Preferably, the semiconducting protective layer contains a binder,a carbon material, and at least one selected from alumina, silica,titania, and zirconia.

In this regard, as for the positive electrode active material usable forthe non-aqueous electrolyte secondary battery according to the inventiondescribed in the present specification, compounds capable of reversivelyoccluding and releasing lithium ions can be appropriately selected andused. As for such positive electrode active materials, lithiumtransition metal complex oxides, which can reversively occlude andrelease lithium ions and which are represented by LiMO₂ (where M is atleast one of Co, Ni, and Mn), that is, LiCoO₂, LiNiO₂,LiNi_(y)Co_(1-y)O₂ (y=0.01 to 0.99), LiMnO₂, and LiCo_(x)Mn_(y)Ni_(z)O₂(x+y+z=1), LiMn₂O₄, LiFePO₄, can be used as the positive electrodeactive material singularly or in a mixed state of two or more amongthem. In addition, a material obtained by adding a hetero metal element,e.g., zirconium, magnesium or aluminum, to a lithium cobalt compoundoxide is also usable.

The solvent of the non-aqueous electrolyte is not specifically limitedand solvents previously employed for the non-aqueous electrolytesecondary battery can be used. For example, cyclic carbonates, e.g.,ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate,and vinylene carbonate (VC); chain carbonates, e.g., dimethyl carbonate(DMC), methylethyl carbonate (MEC), and diethyl carbonate (DEC);ester-containing compounds, e.g., methyl acetate, ethyl acetate, propylacetate, methyl propionate, ethyl propionate, and γ-butyrolactone;sulfone-containing compounds, e.g., propane sultone; ether-containingcompounds, e.g., 1,2-dimethoxyethane, 1,2-diethoxyethane,tetrahydrofuran, 1,2-dioxane, 1,4-dioxane, and 2-methyl tetrahydrofuran;nitrile-containing compounds, e.g., butyronitrile, valeronitrile,n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile,pimelonitrile, 1,2,3-propanetricarbonitrile, and1,3,5-pentanetricarbonitrile; and amide-containing compounds, e.g.,dimethylformamide, can be used. In particular, solvents in which part ofH in these solvents has been substituted with F are used preferably.Also, these solvents can be used alone or in combinations of a pluralityof types. In particular, solvents on the basis of combinations of cycliccarbonate and chain carbonate and solvents on the basis of combinationsof a compound containing a small amount of nitrile or anether-containing compound with them are preferable.

Also, an ionic liquid can be used as the non-aqueous solvent of thenon-aqueous electrolyte. In this case, cation species and anion speciesare not specifically limited. However, from the viewpoint of lowviscosity, electrochemical stability, and hydrophobicity, a combinationby using a pyridinium cation, an imidazolium cation, or a quaternaryammonium cation as the cation and a fluorine-containing imide anion asthe anion is particularly preferable.

In addition, a known lithium salt which has been previously commonlyused for the non-aqueous electrolyte secondary battery can be used as asolute to be used for the non-aqueous electrolyte. Then, a lithium saltcontaining at least one of element of P, B, F, O, S, N, and Cl can beused as such a lithium salt. Specifically, lithium salts, e.g., LiPF₆,LiBF₄, LiCF₃SO₃, LiN(FSO₂)₂, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂,LiN(CF₃SO₂)(C₄F₉SO₂), LiC(C₂F₅SO₂)₃, LiAsF₆, LiClO₄, and LiPF₂O₂, andmixtures thereof can be used. In particular, in order to enhance thehigh rate charge and discharge characteristics and the durability of thenon-aqueous electrolyte secondary battery, it is preferable to useLiPF₆.

Also, a lithium salt, in which an oxalate complex serves as an anion,can be used as the solute. As for the lithium salt in which an oxalatecomplex serves as an anion, besides LiBOB (lithium-bisoxalate borate), alithium salt having an anion in which C₂O₄ ²⁻ is coordinated to thecenter atom, for example, a lithium salt represented byLi[M(C₂O₄)_(x)R_(y)] (in the formula, M represents an element selectedfrom transition metals and group 13, group 14, and group 15 of theperiodic table, R represents a group selected from halogens, alkylgroups, and halogen-substituted alkyl groups, x represents a positiveinteger, and y represents 0 or a positive integer) can be used. Specificexamples include Li[B(C₂O₄)F₂], Li[P(C₂O₄)F₄], and Li[P(C₂O₄)₂F₂].However, in order to form a stable coating film on the negativeelectrode surface even under a high temperature environment, LiBOB isused most preferably.

In this regard, not only the above-described solutes are used alone butalso at least two types may be used in combination.

Meanwhile, the concentration of the solute is not specifically limited,although 0.8 to 1.7 mol per liter of non-aqueous electrolytic solutionis desirable. Furthermore, in the use where discharge at a large currentis required, the concentration of the above-described solute isdesirably 1.0 to 1.6 mol per liter of non-aqueous electrolytic solution.

In the non-aqueous electrolyte secondary battery according to an aspectof the invention described in the present specification, the negativeelectrode active material used for the negative electrode is notspecifically limited insofar as the negative electrode active materialcan reversively occlude and release lithium ions. For example, carbonmaterials, lithium metal, metal or alloy materials which are alloyedwith lithium, metal oxides, and the like can be used. In this regard, itis preferable that carbon materials be used for the negative electrodeactive material from the viewpoint of material cost. For example,natural graphite, artificial graphite, mesophase pitch based carbonfibers (MCF), mesocarbon microbeads (MCMB), coke, and hard carbon can beused. In particular, from the viewpoint of improvement of the high ratecharge and discharge characteristics, it is preferable that the carbonmaterial in which a graphite material is covered with low crystallinecarbon be used as the negative electrode active material.

A known separator which has been previously commonly used for thenon-aqueous electrolyte secondary battery can be used as the separator.Specifically, not only a separator made of polyethylene but also apolyethylene having a surface provided with a polypropylene layer or apolyethylene separator having a surface coated with an aramid resin maybe used.

A layer including an inorganic material filler, which has been usedpreviously, can be disposed at the interface between the positiveelectrode and the separator or the interface between the negativeelectrode and the separator. As for the filler, oxides or phosphatecompounds by using titanium, aluminum, silicon, magnesium, and the likealone or in combination, which have been used previously, and thosehaving surfaces treated with a hydroxide or the like can be used.Meanwhile, as for formation of the filler layer, for example, a methodin which formation is performed by directly applying a filler-containingslurry to the positive electrode, the negative electrode, or theseparator and a method in which a sheet formed from a filler is stuck onthe positive electrode, the negative electrode, or the separator can beused.

In the above-described embodiment and the second invention, thenon-aqueous electrolyte secondary battery in which thepressure-sensitive current shut-off mechanism is disposed in at leastone of the conducting path between the positive electrode plate and thepositive electrode terminal and the conducting path between the negativeelectrode plate and the negative electrode terminal has been explained.It is considered that a non-aqueous electrolyte secondary battery, inwhich a pressure-sensitive forced short-circuit mechanism is disposedinstead of disposition of the pressure-sensitive current shut-offmechanism, is produced.

It is preferable that the forced short-circuit mechanism be disposed inthe vicinity of the negative electrode terminal 20 of a sealing body 23,as shown in FIG. 7. FIG. 8 is a magnified diagram of a portion in whichthe forced short-circuit mechanism 50 is disposed. FIG. 8A shows thestate before actuation of the forced short-circuit mechanism 50, andFIG. 8B shows the state after actuation of the forced short-circuitmechanism.

As shown in FIG. 8A, the metal sealing body 23 has a valve portion 51electrically connected to the positive electrode plate 11, and a tabularelectrically conductive member 52 electrically connected to the negativeelectrode plate 12 is disposed outside this valve portion 51. The valveportion 51 is made of a metal and may be integrally formed with thesealing body 23. Alternatively, the valve portion 51 independent fromthe sealing body 23 may be connected to the sealing body 23. Here, theelectrically conductive member 52 is connected to the negative electrodeterminal 20 and is connected to the negative electrode plate 12 throughthe negative electrode collector 19. In this regard, the electricallyconductive member 52, the negative electrode terminal 20, and thenegative electrode collector 19 are electrically insulated from thesealing body 23 with an insulating member 22.

In the case where the battery is brought into an overcharge state andthe internal pressure of the battery has increased to a predeterminedvalue or more, as shown in FIG. 8B, the valve portion 51 is deformedoutward (upward in FIG. 8B) and comes into contact with the electricallyconductive member 52. The valve portion 51 is made of a metal and iselectrically connected to the positive electrode plate 11, and theelectrically conductive member 52 is electrically connected to thepositive electrode plate 12. Therefore, the positive electrode plate 11and the negative electrode plate 12 are brought into a short-circuitstate by contact of the valve portion 51 and the electrically conductivemember 52. Consequently, flowing of a charging current into theelectrode assembly can be prevented. Also, the energy in the electrodeassembly can be released promptly. In this manner, in the case where thebattery is brought into an overcharge state, the safety can be ensured.

REFERENCE SIGNS LIST

-   -   10 non-aqueous electrolyte secondary battery 11, 11A positive        electrode plate 11 a positive electrode mix layer    -   11 b protective layer 12 negative electrode plate 12 a negative        electrode mix layer    -   13 separator 14, 14A flat rolled electrode assembly 15 positive        electrode core body exposed portion    -   15 a weld trace 16 negative electrode core body exposed portion        17 positive electrode collector    -   18 positive electrode terminal 19 negative electrode collector        20 negative electrode terminal    -   21, 22 insulating member 23 sealing body 24 insulating sheet    -   25 rectangular outer body 26 electrolytic solution injection        hole 27 current shut-off mechanism    -   28 gas discharge valve 29 positive electrode electrically        conductive member 30 positive electrode intermediate member    -   31 negative electrode electrically conductive member 32 negative        electrode intermediate member 33, 34 weld trace    -   50 forced short-circuit mechanism 51 valve portion 52        electrically conductive member

The invention claimed is:
 1. A non-aqueous electrolyte secondary battery comprising: a positive electrode plate in which a positive electrode mix layer is disposed on a positive electrode core body; a negative electrode plate in which a negative electrode mix layer is disposed on a negative electrode core body; a positive electrode terminal electrically connected to the positive electrode plate; a negative electrode terminal electrically connected to the negative electrode plate; a flat rolled electrode assembly in which the positive electrode plate and the negative electrode plate in the state of being insulated from each other with a separator therebetween are rolled into a flat shape; a non-aqueous electrolytic solution; and an outer body, wherein a rolled positive electrode core body exposed portion is disposed at one end portion of the flat rolled electrode assembly, a rolled negative electrode core body exposed portion is disposed at the other end portion of the flat rolled electrode assembly, the rolled positive electrode core body exposed portion is bundled and connected to a positive electrode collector, the rolled negative electrode core body exposed portion is bundled and connected to a negative electrode collector, a pressure-sensitive current shut-off mechanism is disposed in at least one of a conducting path between the positive electrode plate and the positive electrode terminal and a conducting path between the negative electrode plate and the negative electrode terminal, lithium carbonate is contained in the positive electrode mix layer, and a porous protective layer is disposed along the border with the positive electrode mix layer at the position opposite to the separator on at least one surface of the positive electrode core body exposed portion, wherein the protective layer has electrical conductivity and is a protective layer having the electrical conductivity lower than that of the positive electrode core body, and the protective layer contains lithium carbonate.
 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the protective layer is less than or equal to the thickness of the positive electrode mix layer.
 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective layer is disposed adjoining the positive electrode mix layer.
 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective layer is disposed at the position apart from the positive electrode mix layer.
 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective layer contains at least one of alumina particles and graphite particles.
 6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective layer is disposed in such a way that a region not covered with the separator disposed oppositely is generated.
 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium carbonate concentration in the positive electrode mix layer is 0.1 percent by mass or more and 5 percent by mass or less relative to the mass of the positive electrode mix.
 8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the outer body is rectangular.
 9. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective layer contains a binder, a carbon material, and at least one selected from alumina, silica, and zirconia.
 10. A non-aqueous electrolyte secondary battery comprising: a positive electrode plate in which a positive electrode mix layer is disposed on a positive electrode core body; a negative electrode plate in which a negative electrode mix layer is disposed on a negative electrode core body; a positive electrode terminal electrically connected to the positive electrode plate; a negative electrode terminal electrically connected to the negative electrode plate; a flat rolled electrode assembly in which the positive electrode plate and the negative electrode plate in the state of being insulated from each other with a separator therebetween are rolled into a flat shape; a non-aqueous electrolytic solution; and an outer body, wherein a rolled positive electrode core body exposed portion is disposed at one end portion of the flat rolled electrode assembly, a rolled negative electrode core body exposed portion is disposed at the other end portion of the flat rolled electrode assembly, the rolled positive electrode core body exposed portion is bundled and connected to a positive electrode collector, the rolled negative electrode core body exposed portion is bundled and connected to a negative electrode collector, a pressure-sensitive current shut-off mechanism is disposed in at least one of a conducting path between the positive electrode plate and the positive electrode terminal and a conducting path between the negative electrode plate and the negative electrode terminal, lithium carbonate is contained in the positive electrode mix layer, and a porous protective layer is disposed along the border with the positive electrode mix layer at the position opposite to the separator on at least one surface of the positive electrode core body exposed portion, wherein the porosity of the protective layer is larger than the porosity of the positive electrode mix layer.
 11. A non-aqueous electrolyte secondary battery comprising: a positive electrode plate in which a positive electrode mix layer is disposed on a positive electrode core body; a negative electrode plate in which a negative electrode mix layer is disposed on a negative electrode core body; a positive electrode terminal electrically connected to the positive electrode plate; a negative electrode terminal electrically connected to the negative electrode plate; a flat rolled electrode assembly in which the positive electrode plate and the negative electrode plate in the state of being insulated from each other with a separator therebetween are rolled into a flat shape; a non-aqueous electrolytic solution; and an outer body, wherein a rolled positive electrode core body exposed portion is disposed at one end portion of the flat rolled electrode assembly, a rolled negative electrode core body exposed portion is disposed at the other end portion of the flat rolled electrode assembly, the rolled positive electrode core body exposed portion is bundled and connected to a positive electrode collector, the rolled negative electrode core body exposed portion is bundled and connected to a negative electrode collector, a pressure-sensitive current shut-off mechanism is disposed in at least one of a conducting path between the positive electrode plate and the positive electrode terminal and a conducting path between the negative electrode plate and the negative electrode terminal, lithium carbonate is contained in the positive electrode mix layer, and a porous protective layer is disposed along the border with the positive electrode mix layer at the position opposite to the separator on at least one surface of the positive electrode core body exposed portion, wherein the protective layer is disposed in such a way that a region not covered with the separator disposed oppositely is generated.
 12. The non-aqueous electrolyte secondary battery according to claim 1, wherein the porosity of the protective layer is larger than the porosity of the positive electrode mix layer.
 13. The non-aqueous electrolyte secondary battery according to claim 10, wherein the thickness of the protective layer is less than or equal to the thickness of the positive electrode mix layer.
 14. The non-aqueous electrolyte secondary battery according to claim 10, wherein the protective layer contains at least one of alumina particles and graphite particles.
 15. The non-aqueous electrolyte secondary battery according to claim 11, wherein the thickness of the protective layer is less than or equal to the thickness of the positive electrode mix layer.
 16. The non-aqueous electrolyte secondary battery according to claim 11, wherein the protective layer contains at least one of alumina particles and graphite particles.
 17. The non-aqueous electrolyte secondary battery according to claim 11, wherein the outer body is sealed.
 18. The non-aqueous electrolyte secondary battery according to claim 11, wherein a width (W1) of the protective layer in a direction along a rolling axis of the flat rolled electrode assembly is greater than a distance (W2) from an end of the positive electrode mix layer to an end of the separator in a vicinity of a distal end of the positive electrode core body exposed portion. 